A true stereophonic disc record has two distinct orthogonal modulations derived from an original live recording in which a minimum of two separate channels are employed.

B. The Stereophonic Groove

1. The stereophonic groove shall contain two channels of information recorded as orthogonal modulations of a single groove.
2. The 45 degree-45 degree system is the standard. In this system the two mutually perpendicular axes of modulation shall be symmetrically disposed with respect to a normal to the disc surface.
3. The right hand information channel, as viewed by the listener, shall appear as modulation of the out side wall of the groove.
4. When equal in-phase signals are recorded in the two channels they shall result in lateral modulation of the stereophonic groove shall produce equal in-phase acoustical signals.
5. The stereophonic groove contour shall be as recommended in RIAA Dimensional Standards for Disc Phonograph Records, Bulletin E 4.

1. The desirable tip radius of the reproducing stylus for stereophonic disc records is 0.5 mils.
2. The reproducing stylus motion shall be tangent to, or lie in a plane which passes through the record center, and which is inclined at a nominal angle of 15 degrees, clockwise, to a normal to the record at the stylus tip, as viewed from the record c
enter.

DIMENSIONAL STANDARDSDISCPHONOGRAPH RECORDSFOR HOME USE

Bulletin No. E 4

RECORD INDUSTRY ASSOCIATION OF AMERICA

These are dimensional standards to facilitate equipment design and assure interchangeabliity. They are not intended to indicate or imply quality or performance levels.

RECORD INDUSTRY ASSOCIATION OF AMERICA, INC.
ONE EAST 57TH STREET
NEW YORK CITY 22

11 7/8" + 1/32"

Thicknessa. Flush Design

.075" + .010" -.015"

.075" + .010"

.075 + .010"

b. Contour Design(See drawings)

Center Hole Diameter

(Same as 10")

0.286" + 0.001" -0.002"

(Same as 10")

Lead-in Spirals.a. To start at record edgeb. Grooves per inchc. Contour to be same as recording groovesNOTE: In addition, there shall be at least one complete unmodulated groove at recording pitch.

(Same as 10")

16-32

(Same as 10")

Margin Diameter, the outer set-down limit of reproducing stylus

6 25/32"

9 23/32"

11 23/32"

Diameter of Outermost Groove at Recording Pitch

6 5/8" max.

9 1/2" max.

11 1/2" max.

Recording Groove Contour

a. Included Angle

(Same as 10")

90 degrees + 5 degrees

(Same as 10")

b. Bottom Radius

(Same as 10")

0.00025" max.

(Same as 10")

c. Width--Monophonic

(Same as 10")

.0022" -- .0032"

(Same as 10")

d. Width--Stereophonic--Instantaneous

(Same as 10")

.0010" min.

(Same as 10")

Minimum Inside Diameter of Recording

4 1/4"

4 3/4"

(Same as 10")

Runout of Recording Grooves Relative to Center Hole

(Same as 10")

0.050" max.

(Same as 10")

Note: This figure does not imply that a record having this degree of run-out would be acceptable from a quality standpoint. It does provide, for instance, a limit for the maximum sensitivity or a velocity trip when combined with the
pitch of spirals between individual bands.

Lead Out Spiral

(Same as 10")

2 to 6 grooves/inch

(Same as 10")

Note: The number of grooves per inch shall be so chosen that the spiral contains at least one complete revolution. (11/1/61)

Stopping Groove, Closed Concentric Circle

a. Diameter

3 7/8" + 0 - 5/64"

4 3/16" +- 1/32"

(Same as 10")

b. Width

(Same as 10")

0.003" -- 0.006"

(Same as 10")

Direction of Rotation

Clockwise, when observer faces side of record being played.

Rotational Speed

(Same as 10")

33 1/3 RPM

(Same as 10")

Crossover spiral Spiral

The number of grooves joining successive bands on a record shall not be less than 16 per inch.

Outside Diameter

6 7/8" + 1/32"

Thickness

a. Recording area, measured at 4 points from edge 90 degrees apart.

0.026" min., 0.052" max.

b. Label area--see drawing of cross section (attached)

Center Hole diameter to be measured under the weight of the record on a tapered plug guage.

1.504" + 0.002"

Lead-in Spiral

a. To start at record edge

b. Grooves per inch

16-32

c. Shape to be same as recording grooves

Note: In addition there shall be at least one complete unmodulated groove at recording pitch.

Margin diameter, the outer set-down limit of the reproducing stylus

6 25/32"

Diameter Outermost Groove at Recording Pitch

6 5/8" + 0

Recording Groove Contour

a. Included angle

90 degrees + 5

b. Bottom radius

0.00025" max.

c. Width--Monophonic

.0022"--.0032"

d. Width--Stereophonic, Instantaneous

.001" min.

Minimum Inside Diameter of Recording

4 1/4"

Runout of Recording Grooves Relative to Center Hole

.050" max.

Note: This figure does not imply that a record having this degree of run-out would be acceptable from a quality standpoint. It does provide, for instance, a limit for the maximum sensitivity of a velocity trip when combined with th
e pitch of spirals between individual selections.

Lead-out Spiral

a. Grooves per inch

2-5

b. Contour

same as recording grooves except width may increase to 0.006"

Stopping Groove, Closed Concentric Circle

a. Diameter

3 7/8" + 0

b. Width

0.003"--0.006"

Direction of Rotation

Clockwise, when observer faces side of record being played.

Rotational Speed

45 RPM

Crossover Spiral

The number of grooves joining successive bands on a record shall not be less than 16 per inch.